According to Dr Kelly, based on his extensive and authoritative knowledge of Iraq's WMD programme, notably it's biological programme...

and

The only other point that we have elicited from Dr Kelly...

Bearing in mind that this was a letter copied to the top echelon of No 10 advisers, and carries the handwritten note (to Chief of Staff Jonathan Powell)

The Prime Minister may find this of interest

one might suppose that a certain degree of care went into its production.

Which leads me to suppose that the letter is in fact in code, to which the errors noted constitute some kind of key. The other two conclusions are too dreadful to contemplate, surely? Sir Humphrey must be positively spinning right now....